1. Field of the Invention
The present invention relates to the manufacture of skis utilized in winter sports, which are adapted to slide on snow and ice.
2. Description of Background and Relevant Information
Skis in current use generally have a composite structure in which different material are combined in a manner such that each of the materials functions in an optimal fashion, taking into account the distribution of mechanical stresses. Thus, the structure generally comprises peripheral protection elements forming the upper surface and lateral surfaces of the ski, and internal resistance elements or resistance blades, comprising a material having a high mechanical resistance and high rigidity. The structure likewise comprises filling elements such as cores having a honeycomb structure, a sliding sole forming the lower surface of the ski and ensuring good sliding on snow, and the metallic edges forming the lower corners of the ski.
To obtain the appropriate physical characteristics, the manufacturer of modern skis relies upon very diverse materials. To this end the sliding soles are generally made of polyethylene; the honeycomb cores are made of synthetic foam; the edges are made out of steel; the surfaces of the ski are formed of thermoplastic sheets; and the resistance blades are plates of metal or fiber reinforced resins.
A ski is subjected to severe mechanical stresses, requiring good adherence between the various materials constituting the structure.
In the traditional manufacturing techniques of skis by injection, one positions in the interior cavity of a mold, against the peripheral walls of the cavity, the upper and lower elements of the ski, and, if necessary, the lateral elements, and one injects, in the space thus defined by the internal surfaces of the elements, the components of a hardenable foam such as polyurethane foam or phenolic foam. After expanding and hardening, the foam assures the assembly of the elements.
The difficulty resides in the fact that the hardenable foams have mediocre adherence properties with a certain number of materials adapted to constitute the structure of the ski or have certain incompatibilities with these materials. Particularly, one can constitute the interior mechanical reinforcement elements of the ski, or resistance blades, from layers of fibrous material pre-impregnated with thermosetting or thermoplastic resin, in an advantageous manner. When such a pre-impregnated element forms the interior surface of the space adapted to be filled with hardenable foam, the foam tends to infiltrate across the pre-impregnated fibrous material which produces both a substantial alteration of the mechanical resistance properties of the reinforcement element and adherence defects between the core made out of hardenable foam and the other materials of the ski.